Flame-retardant molded composition which incorporates a poly(styrene-co-N-phenylmaleimide-co-dibromostyrene) copolymer

ABSTRACT

A moldable composition which comprises a novel random bromostyrene-containing copolymer and a flame-retardant synergist is disclosed. The molded composition exhibits at least a 94V-1 classification when tested in accordance with Underwriters&#39; Laboratories Inc. Test Method UL94.

This is a division, of application Ser. No. 685,362, filed 12/24/84.

This invention relates to polymers.

In one of its more specific aspects, this invention relates to amoldable polymer composition which, upon molding, exhibits excellentnonflammability properties.

The present invention provides a random bromostyrene-containingcopolymer and a composition which comprises a flame retardant"synergist" in combination with the random styrenic copolymer. Thecomposition upon molding, exhibits at least a 94V-1 classification whentested in accordance with Underwriters' Laboratories Inc. Test Method UL94.

According to this invention there is provided a moldable compositioncomprising a random copolymer comprised of the following recurringunits: ##STR1## wherein each R separately represents --H, --CH₃, or--CH₂ CH₃ ; R¹ represents --CH₃, --CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃, --OH,--NH₂, --OCH₃, --CO₂ H, --CONH₂, or --CON(CH₃)₂ ; each R² separatelyrepresents --H or --CH₃ ; R³ represents a C₁ to C₄ alkyl group, achlorine or bromine substituted C₁ to C₄ alkyl group, or ##STR2## R⁴represents --CH₃, --CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃, --Cl, --Br, --OH,--NH₂, --OCH₃, --CO₂ H, --CONH₂, or --CON(CH₃)₂ ; x represents aninteger of from 0 to 3 and wherein y represents an integer of from 1 to3; and, a flame retardant synergist.

Also, according to this invention there is provided a method forproducing a molded article which comprises (1) blending a randomcopolymer comprised of the following recurring units: ##STR3## whereineach R separately represents --H, --CH₃, or --CH₂ CH₃ ; R¹ represents--CH₃, --CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃, --OH, --NH₂, --OCH₃, --CO₂ H,--CONH₂, or --CON(CH₃)₂ ; each R² separately represent --H or --CH₃ ; R³represents a C₁ to C₄ alkyl group, a chlorine or bromine substituted C₁to C₄ group or; ##STR4## R⁴ represents --CH₃, --CH₂ CH₃, --CH(CH₃)₂,--C(CH₃)₃, --Cl, --Br, --OH, --NH₂, --OCH₃, --CO₂ H, or --CONH₂, or--CON(CH₃)₂ ; x represents an integer from 0 to 3; and, wherein yrepresents an integer of from 1 to 3 and a flame-retardant synergist;and, (2) molding the resulting blend.

According to this invention there is also provided a random copolymercomprised of the following recurring units: ##STR5## wherein each Rseparately represents --H, --CH₃, or --CH₂ CH₃ ; R¹ represents --CH₃,--CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃, --OH, --NH₂, --OCH₃, --CO₂ H, --CONH₂,or --CON(CH₃)₂ ; each R² separately represents --H or --CH₃ ; R³represents a C₁ to C₄ alkyl group, a chloride or bromine substituted C₁to C₄ alkyl group or ##STR6## R⁴ represents --CH₃, --CH₂ CH₃,--CH(CH₃)₂, --C(CH₃)₃, --Cl, --Br, --OH, --NH₂, --OCH₃, CO₂ H, --CONH₂,or --CON(CH₃)₂ ; x represents an integer of from 0 to 3; and, wherein yrepresents an integer of from 1 to 3.

In a preferred embodiment of this invention, the total amount ofchlorine and/or bromine in the random copolymer will be within the rangeof from about 2 to about 16 weight percent, preferably, it will bewithin the range of from about 3 to about 12 weight percent.

In another embodiment of this invention the random copolymer is apoly(styrene-co-N-phenylmaleimide-co-aibromostyrene).

In another embodiment of this invention, the random copolymers can befoamed using any conventional method for foaming polmers such as, forexample, extruding the random copolymer in contact with a conventionalfoaming agent or impregnating the copolymer with a foaming agentfollowed by heating the impregnated copolymer above its glass transitiontemperature.

In another embodiment the moldable composition of this invention whichis comprised of a random copolymer and a synergist is employed as aflame-retardant blending component for thermoplastic resins; thecomposition serving as a flame-retardant for the resin. The compositionof this invention can be blended with any suitable thermoplastic resinincluding styrene/maleic anhydride, styrene/acrylonitrile, polyphenyleneoxide, styrene/N-phenylmaleimide, polyvinyl chloride, polycarbonate,polysulfone, polyarylate, polyester, polyamides and the like and theirmixtures. Impact modified resins are also suitable such as, for example,rubber modified styrene/maleic anhydride copolymer.

The amount of random copolymer-synergist composition employed whenblended with a thermoplastic resin is that amount effective to enhancethe fire-retardant properties of the thermoplastic resin upon molding ascompared with the flame-retardant properties of the thermoplastic resinin the absence of the random polymer-synergist composition. Typically,when employed as a flame retardant component, the randomcopolymer-synergist composition will be present in an amount within therange of from about 5 to about 50 weight percent based on the weight ofthe total composition.

In the practice of the invention, any suitable monomers can be employedto produce the first depicted recurring monomeric unit in the abovegeneral structure of the copolymer. Suitable monomers include: styrene,α-methylstyrene, α-ethylstyrene, methylstyrene, isopropylstyrene,t-butylstyrene, vinylbenzoic acid, vinyl phenol, vinyl analine,nitrostyrene, cyanostyrene, methoxystyrene, α-methyl-4-cyanostyrene,α-4-methylstyrene and the like, and their mixtures. Styrene is thepreferred monomer. The random copolymer will comprise of from about 5 toabout 85 weight percent recurring units of this monomer.

In the practice of this invention, any suitable monomers can be employedto produce second depicted recurring monomeric unit in the above generalstructure. Suitable monomers include: N-methylmaleimide,N-phenylmaleimide, N-phenylcitraconimide,N-phenyl-3,4-dimethyl-maleimide, N-(4-bromophenyl) maleimide,N-(2,4,6-tribromophenyl) maleimide, N-(4-chlorophenyl) maleimide,N-(4-cyanophenyl) maleimide, N-(4-hydroxyphenyl) maleimide,N-(4-aminophenyl) maleimide, N-(4-methoxyphenyl) maleimide,N-(4-benzamide) maleimide and the like, and their mixtures.N-phenylmaleimide is most preferred. And, although an alkyl or arylsubstituted maleimide is preferred, maleimide may also be used. Therandom copolymer will comprise of from about 1 to about 62 weightpercent recurring units of this monomer.

In the practice of this invention, any suitable brominated styrenemonomer can be employed as the third depicted recurring monomeric unitin the above general structure. Suitable bromostyrenes include:monobromostyrene, dibromostyrene, tribromostyrene,α-methyl-2,4,6-tribromostyrene, α-ethyl-4-bromostyrene and theirmixtures. The random copolymer will comprise of from about 4 to about 94weight percent recurring units of this monomer.

a particularly suitable brominated styrene is available from Great LakesChemical Corporation and designated Great Lakes Dibromostyrene.

Great Lakes Dibromostyrene is a reactive monomer containing 61% aromaticbromine having the following general formula ##STR7## and exhibiting thefollowing typical properties:

    ______________________________________                                        appearance      light yellow liquid                                           density         1.82 g/ml                                                     boiling point   95° C. (at 3 mm Hg)                                    assay, %        99+ brominated styrenes                                       isomers         dibromo 80%                                                                   monobromo 10%                                                                 tribromo 10%                                                  ______________________________________                                    

If the random copolymer of this invention is used to produce moldedarticles the number average molecular weight of the copolymer should beat least 30,000, preferably at least 80,000 to about 500,000.

To produce a moldable composition of this invention the random copolymercan be conventionally blended with any suitable flame-retardantsynergist. The synergist will typically be employed in an amount withinthe range of from about 1 to about 10, preferably from about 1 to about5 weight percent of the composition (copolymer plus synergist).

Suitable synergists include: antimony trioxide, antimony pentoxide,arsenic trioxide, arsenic pentoxide, zinc sulfate, zinc oxide, zincborate, bismuth oxide, molybdenum oxide, tungsten oxide, stannous oxideand the like, and their mixtures. The preferred synergist is antimonytrioxide.

Optionally, the molding composition can include other ingredients. Suchas extenders, smoke suppressants, antioxidants, reinforcing fillers,processing aids, pigments, stabilizers, mold release agents and thelike, for their conventionally employed purpose.

The N-(brominated or chlorinated phenyl)maleimides which are suitablefor use as one of the recurring monomeric units in the random copolymersof this invention are not known to be commercially available.Accordingly, Example I demonstrates the preparation ofN-(2,4,6-tribromophenyl)maleimide.

This invention is further demonstrated by the following examples.

EXAMPLE I

This example demonstrates the preparation ofN-(2,4,6-tribromophenyl)maleimide.

Into a reaction vessel were added and mixed 100 g. (0.303 mole) of2,4,6-tribromoanaline, 68.34 g (0.697 mole) of maleic anhydride, and5.16 g (0.379 mole) of zinc chloride.

The resulting mixture was heated at a temperature within the range offrom about 139° to 148° C. for about 2 hours.

The resulting reaction product was extracted with xylene, filtered andwater washed.

The xylene solvent was removed and the resultant productN-(2,4,6-tribromophenyl)maleimide was recovered at a yield of about 94%.

EXAMPLE II

This example demonstrates the preparation of a copolymer of thisinvention which contains recurring units of styrene, N-phenylmaleimideand dibromostyrene.

Into a one-gallon stirred reactor were charged 2367 g of methyl ethylketone, 313 g styrene, 577 g N-phenylmaleimide and 125 g of Great LakesDibromostyrene monomer.

About 0.8 g of benzoyl peroxide was added to the reaction mixture andthe mixture heated to 75° C.

The resulting polymerization reaction was allowed to proceed for fivehours, and then 5 g of butylated hydroxy toluene ("BHT") were added.

The copolymer was recovered by precipitation from methanol, filtered,washed with methanol and dried under vacuum.

The recovered random copolymer was found to contain 54.3%N-phenylmalemide and 9.8% dibromostyrene (6.0% bromine).

The copolymer was found to have a glass transition temperature of 224°C. (by Differential Scanning Calorimetry "DSC"), a number averagemolecular weight of 147,000 and a weight average molecular weight of367,000 as measured by gel permeation chromotography using polystyrenestandards.

EXAMPLE III

This example demonstrates the preparation of a copolymer of thisinvention which contains recurring units of styrene, N-phenylmaleimideand dibromostyrene.

Into a one-pint citrate bottle were charged 57.4 g N-phenylmaleimide,33.3 g styrene, and 5.5 g Great Lakes Dibromostyrene monomer.

Next, about 0.03 g benzoyl peroxide initiator was added.

The bottle was flushed with nitrogen, tightly sealed and placed in abottle polymerizer at 90° C. and polymerization was allowed to proceedfor 2.5 hours.

The resultion copolymer was dissolved in THF and precipitated inmethanol, filtered, washed with methanol and dried under vacuum.

The copolymer exhibited a glass transition temperature of 206° C. (byDSC) and was found to contain 51% N-phenylmaleimde and 5.7%dibromostyrene (3.5% bromine).

EXAMPLE IV

This examples demonstrates the preparation of a copolymer of thisinvention which contains recurring units of styrene,N-(2,4,6tribromophenyl)maleimide and dibromostyrene.

Into a one-gallon stirred reactor is charged 2367 g of methyl ethylketone, 313 g styrene, 577 g of the N-(2,4,6-tribromophenyl)maleimideproduced in Example I and 125 g of dibromostyrene monomer (Great Lakes).

About 0.8 g of benzoyl peroxide is added to the reaction mixture and themixture is heated to 75° C.

The resulting polymerization reaction is allowed to proceed for fivehours, and then 5 g of BHT are added.

The copolymer is recovered by preicipitation from methanol, filtering,washing with methanol and drying under vacuum.

EXAMPLE V

The copolymers produced in Examples 2 and 3 were separately melt blended(at 550° F. and 530° F., respectively) with 4% antimony trioxide basedon the weight of the total composition (copolymer plus synergist). Theresulting blends were separately molded and the molded blends weretested for flammability in accordance with Underwriters Laboratories UL94 (UL 94 Standard for Tests for Flammabiliy of Plastic Materials ForParts in Devices and Appliances, UL 94, third edition Jan. 24, 1980).

In this UL 94 Vertical Burning Test, the molded copolymer test specimenwas supported from the upper end, with the longest dimension vertical,by a clamp on a ring stand so that the lower end of the specimen was 1"above the top of the burner tube. The burner was then placed remote fromthe sample, ignited, and adjusted to produce a blue flame 1" in height.The test flame was placed centrally under the lower end of the testspecimen and allowed to remain for 10 seconds. The test flame was thenwithdrawn, and the duration of flaming or glowing combustion of thespecimen was noted. If flaming or glowing combustion of the specimenceased within 30 seconds after removal of the test flame, the test flamewas again placed under the specimen for 10 seconds immediately afterflaming or glowing combustion of the specimen stopped. The test flamewas again withdrawn, and the duration of flaming or glowing combustionof the specimen was noted. If the specimen dripped flaming particles ordroplets while burning in this test, these drippings were allowed tofall onto a horizontal layer of cotton fibers (untreated surgicalcotton) placed one foot below the test specimen. Significantly flamingparticles were considered to be those capable of igniting the cottonfibers. The duration of flaming or glowing combustion of verticalspecimens after application of the test flame (average of 5 specimenswith 10 flame applications) should not exceed 25 seconds (maximum notmore than 30 seconds) and the portion of the specimen outside the clampshould not be completely burned in the test.

Materials which comply with the above requirements and do not drip anyflaming particles or droplets during the burning test are classified as"V-1". Materials which comply with the above requirement but dripflaming particles or droplets which burned briefly during the test areclassified as "V-2". A "V-0" rating is given to materials wherein theduration of flaming or glowing combustion averages less than 5 secondsunder the conditions specified above.

the results of the UL 94 testing was as follows:

    ______________________________________                                        Molded Composition of                                                                         UL 94 (5" × 1/2" × 1/8" bar)                      ______________________________________                                        Example 2       V-0                                                           Example 3*      V-0                                                           ______________________________________                                         *Due to small quantity of polymer only 2 specimens tested                

It will be evident from the foregoing that various modifications can bemade to this invention. Such, however, are considered as being withinthe scope of the invention.

What is claimed is:
 1. A method for producing a molded article whichcomprises (1) blending a random copolymer comprised of the followingrecurring units: ##STR8## wherein each R separately represents --H,--CH₃, or --CH₂ CH₃ ; R¹ represents --CH₃, --CH₂ CH₃, --CH(CH₃)₂,--C(CH₃)₃, --OH, --NH₂, --OCH₃, --CO₂ H, --CONH₂, or --CON(CH₃)₂ ; eachR² separately represents --H or --CH₃ ; R³ represents a C₁ to C₄ alkylgroup, a chlorine or bromine substituted C₁ to C₄ group, or ##STR9## R⁴represents --CH₃, --CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃, --Cl, --Br, --OH,--NH₂, --OCH₃, --CO₂ H, --CONH₂, or --CON(CH₃)₂ ; x represents aninteger from 0 to 3; and, wherein y represents an integer of from 1 to3; and, a flame-retardant synergist and, (2) molding the resultingblend.
 2. The method of claim 1 comprising molding said blend in contactwith a reinforcing filler.